a small device that plugs into a computer and serves as an adapter or as a security measure to enable the use of certain software

Pronunciation:
DONG-ul

In a sentence:
Jerry spent the day hunting for a dongle so that he could play the latest version of the hot new web-based video game, Communist Crusher 8000.

In a different sentence:
Without her dongle Rebecca couldn’t gain access to the World Domination software she had created in her spare time, and therefore had to continue working as a clerk at a fish store and eating (very fresh) fish sticks for dinner every night.